The present invention relates generally to apparatus and methods for reinforcing existing tower structures interior.
Existing towers, including guy-wired or self-supporting towers for supporting communication devices and antennas, for example, may require reinforcing because they weaken over time or the desired to enable additional load-bearing capabilities of the tower. When the term “load” is used herein, it is understood to mean shear forces from wind and compression in addition to the weight that is supported by a structure. Typically, each tower has its own foundation and multiple legs which are spliced together at convenient intervals, with diagonal and horizontal cross-braces interspersed between the legs. The splice connections for each tower section typically are constructed in one of two ways. The first type of splice connection is accomplished using abutting flange plates having matching bolt hole placements. The second type of splice connection, used for those towers having tubular legs, incorporates a telescoping connection of the two tubular legs, where the end of one leg in cross-section is reduced so that it fits inside the corresponding leg in order that matching bolt holes can be aligned for connecting the two legs.
It would be desirable to have a way of increasing the structural integrity and capability of existing towers in lieu of replacing the towers entirely. Previous attempts to bolster existing tower structures have provided augmentation members which are installed on the existing tower legs. In such a structure, addition of such devices as antenna to the tower structure is impaired by the location of the augmentation of additional members attached to the existing tower legs. Thus, a need exists for apparatus and methods for reinforcing an existing tower structure that does not require structural modification such as field drilling or field welding to existing the tower legs and allows continued access to existing tower legs.
U.S. Pat. No. 1,658,535 issued to Neilson discloses a derrick wherein tension rods 29 having “hooked” or “eyed” ends (shown in FIG. 4) are used to connect the clamp brackets 8 to the base 32 and to an upper section 2′ of the derrick. This is replicated throughout the entire length of the derrick. These tension rods 29 are discussed, for example, at page 2, line 21 and 45, and at page 3 lines 14, 27, 52, 65, 75, 77 and 105. The Neilson patent does not disclose or suggest apparatus or methods that provide for a reduction of the compression load on load-bearing sections of an existing lattice tower. The Neilson patent does not address this, because the leg members are held in tension by the tension rods with their hooked or eyed ends. There is no disclosure or suggestion contained in the Neilson patent that would address compression load reduction. There is also no disclosure or suggestion contained in the Neilson patent that would address reinforcing existing tower structures.
U.S. Pat. No. 4,216,636, issued Aug. 12, 1980, discloses a tower characterized by a rigid, self-supporting structure which includes a set of vertically oriented outside legs arranged in a generally triangular configuration and a set of vertically oriented inside legs also arranged in a generally triangular configuration and positioned adjacent the outside legs. This arrangement provides for coaxial inner and outer triangular-shaped support structures. The outside legs and inside legs are fitted with a plurality of generally horizontally disposed braces and are supported in spaced relationship by a plurality of triangular collars also oriented in generally horizontal and spaced relationship along the length of the tower. In a preferred embodiment the outside legs and inside legs are fastened to the triangular collars by means of flanges. The triangular collars are solid and secure all six inside and outside legs. The triangular collars are installed when constructing the coaxial tower structure, and there is no disclosure or suggestion that they could or should be added subsequent to construction. Also, nothing is disclosed or suggested in U.S. Pat. No. 4,216,636 regarding a triangular coaxial tower reinforcing structure that is added to an existing tower structure to reinforce it.
U.S. Pat. No. 2,945,231 issued to Scheldorf cited in the Background section of U.S. Pat. No. 4,216,636 discloses antenna tower having coaxial inner and outer support structures with triangular-shaped cross sections, as illustrated in FIG. 3. The inner structure is the primary structural member of the tower and the outer members characterize a suppressor structure. The legs of the tower are securely anchored in concrete for maximum rigidity and the triangular cross-sectional configuration of the structure insures maximum strength. However, nothing is disclosed or suggested in U.S. Pat. No. 2,945,231 regarding a tower reinforcing structure that is constructed and added to an existing tower structure to reinforce it.
Inventions that improve upon prior reinforcement techniques are disclosed in U.S. Pat. No. 6,935,025, issued Aug. 30, 2005, and U.S. Pat. No. 6,944,950, issued Sep. 20, 2005, for example. These patents discloses apparatus and methods for reinforcing at least one load-bearing section of an existing lattice tower assembly, which load-bearing section has a predetermined compression load.
Exemplary apparatus and methods disclosed in U.S. Pat. No. 6,935,025 provide for two leg members, and at least one brace member, sized and configured for connection to both of the leg members. At least one connecting plate is sized and configured for attachment to a respective flange plate of the section of the tower assembly and for attachment to an end of one of the leg members, which flange plate is attached to or integral with the section of the tower assembly. The leg members, the at least one brace member and at least one connecting plate are sized and configured for attachment to one another to form a structure or a plurality of structures, such that the two leg members bear at least a portion of the compression load when installed.
Transfer means transfers a portion of the compression load from the one or more load-bearing sections to the leg members so that the one or more load-bearing sections have a compression load that is lower than the predetermined compression load.
Exemplary apparatus and methods disclosed in U.S. Pat. No. 6,944,950, and illustrated in FIGS. 3, 8A and 8B, for example, provide for three pairs of outer reinforcing leg members comprising a plurality of connectable leg sections respectively located outside of, or exterior to, three existing leg members of the tower assembly. One reinforcing leg member from each pair is interconnected to a proximal reinforcing leg member of an adjacent pair using braces to form a load bearing structure. Threaded sleeve nuts and lock nuts axially interconnect adjacent ones of the connectable leg sections and are used to adjust the overall length of the associated leg member, and thus transfer a portion of the compression load from the load-bearing section to the outer leg members so that the load-bearing section has a compression load that is lower than the predetermined compression load. The compression load that is transferred to the outer legs is shifted away from the axial centerline of the tower assembly and toward the outside of the tower assembly.
The tower reinforcement apparatus disclosed in U.S. Pat. No. 6,944,950 adds additional legs and reinforcing structures to the exterior of the existing tower. Nothing is disclosed or suggested in U.S. Pat. No. 6,944,950 indicating the desirability, benefits, or usefulness of reinforcing leg members and reinforcing structures located inside the locations of existing tower legs, closer to the vertical center of the tower. However, towers can become highly loaded along their exterior edges, such as when additional or larger communication antennas are installed. This loading also may not be symmetrical. The present invention addresses the issue of exterior tower loading.
In addition, the vast majority (if not all) of the antennas and cables attached to the tower are affixed to the exterior of the tower, and reinforcing members placed on the exterior perimeter of the tower may be in physical conflict with the antennas and cables.
It would be desirable to improve upon the apparatus and methods disclosed in U.S. Pat. No. 6,944,950, for example, and other patented techniques, to reinforce antenna towers that are highly loaded on the exterior. It would be desirable to have reinforcement methods and apparatus that provide attachable structures that do not require welding or drilling. It would be desirable to have reinforcing methods and apparatus that, once installed, allows continued access to the existing tower legs so that later attachment of communication devices are not impeded. It would be desirable to have reinforcement methods and apparatus that accomplishes the reinforcement process completely on site, or allows partial offsite assembly in another location before final installation in the field. It would be desirable to have reinforcement methods and apparatus that would allow the original safety line attachments to remain place. It would also be desirable to have reinforcement methods and apparatus that address problems associated with exterior loading of towers. It would be desirable to have reinforcement methods and apparatus that shifts the compression loading toward the center of the tower.